Preheat your oven to 400 F/ 200 C. Line a baking sheet with parchment paper and set it aside. Roughly chop the tomatoes, onion, and garlic and transfer them to a bowl.
Add the olive and chili flakes to the bowl. Season with salt and pepper, and toss to mix. Taste seasoning and adjust if needed.
Spread the seasoned vegetables onto the baking sheet, leaving the excess liquid in the bowl. Transfer the sheet to the oven. Roast for 15-20 minutes, or until the edges are dark.
Transfer the roasted tomatoes, onions, and garlic to a medium saucepan over medium heat. Add the vegetable stock and basil and bring the soup to a simmer. Let it cook for 5 more minutes.
Using an immersion blender, puree the vegetables until smooth. Taste and adjust seasoning if needed. You can pass the soup through a fine sieve if you want a silky-smooth soup.
Add the coconut milk and stir. Divide the soup into 4 bowls, and garnish with a drizzle of coconut milk and basil leaves. Serve immediately.